A week ago Microsoft pushed out an unlucky update (Cumulative Update KB3194496) to members of the Windows Insider Program that caused an endless reboot loop on the PCs of a subset of users. In an explanation to ZD Net, Microsoft claims the issue occurs on systems that previously ran a build delivered through the Windows Insider Program and were later switched to the public Current Branch release.
The terse description of the file describes it simply: "Script to fix Xbox Scheduled Task leftover regkeys that blocks update for insider builds prior to 14388." There's no indication of how many systems were affected, but the number is probably in the hundreds of thousands, representing systems that were in the Windows Insider Program, receiving preview releases, during the first half of 2016 before switching to the public branch.
Although that number is small, it represents an unusually influential group of Windows 10 users, including a fair number of tech reporters who specialize in Microsoft topics.